1. Field of the Invention
The present invention relates to a variable angle wobble plate type compressor including a suction chamber, discharge chamber, and a crankcase, wherein a piston stroke is varied through a change in an inclination of the wobble plate from a fully inclined position to a substantially non-inclined position nearly vertical to a drive shaft of the compressor, which change is caused by a pressure difference between a suction pressure and a crankcase pressure. More particularly, the present invention relates to an improved wobble angle control unit for changing a compressor displacement, whereby the change in an inclination of the wobble plate is smoothly controlled from the non-inclined position to the fully inclined position.
2. Description of the Related Art
The U.S. Pat. No. 4,685,886 by K. Takenaka et al, discloses a typical variable angle wobble plate type compressor with wobble angle control unit. This compressor is applicable to a refrigerant compressor unit of, for example, an automobile air-conditioning system which includes the refrigerant compressor unit, a condenser unit, an expansion valve unit, and an evaporator unit. When the compressor is used for air-conditioning the automobile compartment, the compressor displacement can be changed in response to a change in a cooling load of the automobile compartment, to regulate the refrigerating function of the air-condition system. A typical variable angle wobble plate type compressor includes a suction chamber for a refrigerant, a plurality of cylinder bores arranged so as to surround an axial drive shaft and having therein reciprocatory pistons disposed so as to draw the refrigerant from the suction chamber and to then discharge the compressed refrigerant in the discharge chamber, a crankcase having defined therein a chamber communicating with the cylinder bores and containing therein a drive plate mounted in such a manner that it is capable of rotating with the axial drive shaft as well as changing an inclination thereof with respect to the axial drive shaft and a non-rotating wobble plate held by the drive plate, a plurality of connecting rods connecting between the wobble plate and pistons, a first passageway for communicating the crankcase chamber with the discharge chamber, a first valve unit arranged in the first passageway, for opening and closing the first passageway, a second passageway for providing a first constant fluid communication between the crankcase chamber and the suction chamber, thereby suppressing an excessive pressure rise in the crankcase chamber that might be caused by a blow-by gas leaking from the cylinder bores into the crankcase chamber, a valve control unit for controlling the operation of the first valve unit in response to a chamber in fluid pressure in the crankcase chamber with respect to a predetermined pressure level in such a manner that when a pressure in the crankcase chamber is less than the predetermined pressure level, the first valve unit is moved to a first position opening the first passageway, and when the pressure in the crankcase chamber is larger than the predetermined pressure level, the first valve unit is moved to a second position closing the first passageway, a third passageway arranged separately from the second passageway, for providing a second variable fluid communication between the crankcase chamber and the suction chamber, the third passageway including a passageway portion thereof extending axially through the drive shaft and in constant communication with the suction chamber, and an open end located in a circumference of the drive shaft so as to open toward the crankcase chamber, and an annular sleeve element slidably mounted on the drive shaft for closably opening the open end of the third passageway in direct relation to a decrease in the inclination of the drive and wobble plates from a predetermined inclined position at which the wobble plate is able to provide the pistons with the maximum reciprocatory strokes. However, in the construction of the typical variable displacement wobble type compressor, the above-mentioned open end of the third passageway extending through the drive shaft is relatively small. Also, in some cases, the open end located in the circumference of the drive shaft is disposed so as to open toward the crankcase chamber, via a tiny hole formed in one of a pair of connecting pins about which the drive plate is pivotally mounted on the sleeve element. Accordingly, the third passageway communicating between the crankcase chamber and the suction chamber is sometimes clogged with the refrigerant per se, especially when the compressor is operating at a low cooling load condition. This is because, when the cooling load is low, since the refrigerant is returned to the compressor from the air-condition circuit without a sufficient thermal exchange at the evaporator in the air-conditioning system, the refrigerant is in the liquid phase when drawn into the compressor. As a result, the liquid refrigerant becomes sticky due to the oil component contained in the refrigerant. Therefore, the sticky refrigerant is apt to stick to the wall of the third passageway and thus cause clogging. When the third passageway is clogged, the wobble angle controllability of the wobble control unit of the wobble plate type compressor must be deteriorated, even if the second passageway contributes to a suppression of an excessive rise in the pressure within the crankcase chamber.